Production of all skin rayon



United States Patent PRODUCTION OF ALL SKIN RAYON Marion R. Lytton, West Chester, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Application June 29, 1955 Serial No. 518,987

6 Claims. 01. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged akali cellulose is then converted to a xanthate by treatment with carbon disulfide. Thecellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containin zinc sulfate. ment may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent difierences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resisance and a low flex-life, is subjected to fibrillation and is relatively stifi.

It has now been discovered that the presence of small amounts of alkali-soluble alkylene oxide adducts of p,pdiphenol in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets, and the like composed of all skin and having improved properties and characteristics providing that the amount of the adduct is maintained within certain limits and the composition of the spinning bath is maintained within certain composition limits which will be The fila- 7 defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of such compounds as are more technically classed as polyoxyalkylene glycol ethers of p,p'-diphenol such as, for example, the ethers of ethylene and propylene glycols and p,p-diphenol. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the polyoxyethylene glycol ethers or ethylene oxide adducts of p,p-diphenol are preferred. Accordingly, the invention will be illustrated specifically by reference to the polyoxyethylene glycol ethers of phenol.

The polyoxyethylene content of the adducts or ethers may vary from about 2 to 50 and more ethylene oxide units per molecule of p,p-diphenol, the preferred ethers containing from about 6 to about 30 ethylene oxide units per molecule. The ether may be conveniently added to the viscose in the form of a solution in alkali or in water.

The amount of the ether or adduct which is incorporated in the viscose must be at least about 0.5% by weight of the cellulose and may vary up to about 4%, preferably, the amount varies from about 1% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The ether or adduct may be added at any desired stage in the production of the viscose, preferably being added after the cellulose xanthate has been dissolved in the caustic solution.

The viscose may contain from about 4% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. containing the small amount of the ether or adduct, may have a sodium chloride salt test above about 7 and preferably above about 9 at the time of spinning or extrusion.

The term salt test as used herein refers to the conven- The presence of the alkylene oxide adducts of p,

diphenol in the viscose combined with these limited spinnin g baths results in the production of yarns of improved properties such as high abrasion resistance, high fatigue res stance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the Zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about C., preferably between about 45 C. to about 70 C. As is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained The modified viscose, that is, a viscose -ofuthe acid concentration, as is well known in the art,

is just above the slubbing point,- that is, the concentration 'at which small slubs of unc-oagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the concentration at which the,

neutralization of the caustic of the viscose is sufficiently rapid to form a filament'having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufiiciently rapid'toproduce filaments having a skin and core. For exa'mple,'in general, the acid concentration of the spinning baths which are satisfactory for the commercial production of the all skin products from a 7% cellulose, 6% caustic viscose containing the ethers of p,p-diph'enol lies between about 6% and about 8.5%. The acid concentration may be increased as the amount of additive'is increased and'also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. All skin'products cannot be obtained if the acid content of the bath is increased above the maximum value although the amount of added ether or. modifier is increased beyond about 4% while other conditions are maintained constant. For example, a viscose containing about 7.5% cellulose, about 6.5% caustic. soda, about 41% carbon disulfide and 1% of a polyoxyethylene glycol ether of p,p'-diphenol containing. about 20 ethylene oxide units.

per molecule and having a salt test of 9 to 10 when textruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% Zinc sulfate and sulfuric acid not more thanabout 8.6%, results in the production of all skin filaments;- Lesser amounts of sulfuric acid may be employed; fGreate'r amounts of acid result in the production of products having skin and core. It has been determined that the maximum p er missible aci-d content of the bath is approximately 1.36 times the caustic soda content of the viscose and is preferably maintained between about 1.2 and 1.3 times the caustic soda content of the viscose.

A lowering" of the amount of'additive, the lowering of the caustic soda content or the lowering of the salt test of theviscose reduces the maximum permissible acid concentration for theproduction'o f all skin filaments.

The presence of the adducts orethers in the viscose.

retards the coagulation and, therefore, the amount of ether employed must be reduced at highspinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, .the adduct is employed in amounts within the lower-portion of the range, for example, about 1%. 'The' determination of' the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiicient to efiect relatively complete coagulation of the viscose, that is, the coagulation must be sulficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the 4 u I preferably between 80% and 100%. Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments. and yarns but it is also applicable 'to other shaped bodies such as sheets, films, tubes and the like.

The filaments may then be passed through a final rea generating bath which may contain from about 1% to about 5% sulfuric acid, and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step,"a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be'dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filamentsprepared from viscose; 1

containing the small amounts of the alkali-soluble alkylene oxide adducts of p,P'-diphenol or the polyoxyalkylene glycol ethers of p,p-diphenol and spun in the spinning baths of limited acid contenthave a smooth or noncrenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section oflthe filament.

containing the alkyl'ene oxide adducts of p,p'-diphenol have high. abrasion and fatigue resistance characteristics r anda high fiex life as compared to normal regenerated cellulose. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber w products such as pneumatic tire casings, but the filaments textile applications; j

'The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a are not restricted to such uses and may beused for other viscose containing about 7.4% cellulose, about 6.6%

caustic soda, and having a total .carbon disulfide content of about 36% based on the weight of the cellulose. The

viscose solutions were prepared by-xanthating alkali cellulose by the introduction of 36% carbon disulfide, based on the weight of the cellulose, and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The polyoxyethylene glycol ether of p, p'-diphenol. was added tothe caustic soda solution and mixed for about /2 hour. lowed to ripen for about 30 hours at 18 C.

Example 1 7 employed in the spinning of filaments hada "salt test of 9.9; The viscose was extruded'thr'ougha spinneret to form a 200 denier, filament yarn at a rate of about 22 meters, per' minute." The coagulating and regenerating 1 bath was maintained at a temperatureof about 60" C.

The viscose was then al- 7 and contained 8.1% sulfuric acid, zinc sulfate and 16% sodium sulfate. The yarn was passed over a godet from which it was conducted through a hot water bath maintained at about 95 C. During the travel through the hot water bath, the yarn was stretched approximately 82%. The yarn was then collected ina spinning box, washed free of acid and salts and dried.

The individual filaments formed from viscose containing the ether of phenol have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e. g. l500 The filaments of the control yarn exhibit a very irregular and serrated surface and are composed of about 55% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows Example 3.

Example 2 Approximately 1% of a polyoxyethylene glycol ether of p,p'-diphenol, containing about 20 ethylene oxide units per molecule of phenol, was added to and incorporated in the viscose as described above. The viscose had a salt test of 9.9 and was spun into a 200 denier, 100 filament yarn by extrusion into a bath containing 8.5% sulfuric acid, 5% zinc sulfate and 16% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 43 meters per minute. The yarn was passed over a godet from which it was conducted through a hot water bath maintained at about 95 C. During the travel through the hot water bath the yarn was stretched about 74%. The yarn was then collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 55% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows Example 3.

Example 3 A control yarn was formed from a viscose as described above without first adding an adduct of p,p-diphenol. The viscose employed in the spinning of filaments had a salt test of 9.7 and was extruded through a spinneret to form a 200 denier, 120 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 8.1% sulfuric acid, 5% zinc sulfate and 16% sodium sulfate. The yarn was passed over a godet from which it was conducted through a hot water bath maintained at about 95 C. During the travel through the hot water bath, the yarn was stretched approximately 82%. The yarn was then collected in a spinning box, washed free of acid and salts and dried.

The individual filaments formed from viscose containing no ether of p,p-diphenol exhibit a very irregular and serrated surface and are composed of about 55% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are included in the table which follows.

The improvements in the physical properties of viscose rayon and other shaped products obtained by the incorporation of the polyoxyethylene glycol ethers of p,p'- diphenol in the viscose are apparent from the table which follows, the data being also representative of the general improvements for other polyoxyalkylene glycol ethers of p,p-diphenol containing different amounts of ethylene oxide:

Tenacity, Elongation, Grains per percent denier Skin,

percent Wet Dry Wet Dry Example 1 2. 37 3.10 25 19 100 0. 79 1. 65 18 17 100 1. 82 2. 73 22 18 55 Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, they consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about for rayon produced by convetnional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The ethers of p,p'-diphenol may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts or ethers may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportion of the additive at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuifs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regen erated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.5% to about 4%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of p,p' diphenol into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zine sulfate and sulfuric acid, the percentage sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 1.36 times the percentage caustic soda content of the viscose.

2. The step in the method as defined in claim l wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of p,p'-diphenol containing from about 6 to 30 ethylene oxide units per molecule of p,p-diphenol.

3. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in viscose from about 0.5% to about 4% of an alkali-soluble polyoxyalkylene glycol ether of p,p'-diphenol, the amount being based upon the weight of the cellulose, and extruding the viscose into 'an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the percentage sulfuri'c acid content of the spinning bath exceeding the slabbing point but not xceeding about 1.36 times the percentage caustic soda content of the viscose.

4. The method as defined in claim 3 wherein the polyoxyalkyle'ne glycol ether is a polyoxyethylene glycol ether cose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15 zinc sulfate and sulfuric acid, the percentage sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 1.36 times the percentage caustic soda content of the viscose.

6. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in aviscose from about 1% to 2%.of an alkali-soluble polyoxyethylene glycol ether of p,p '-diphenol, the amount being based upon the weight of the cellulose, the ether containing from about 6 to 30 ethylene oxide units per molecule of p,p'-

diphenol, ripening the viscose to a sodium chloride salt point of not less than 9 and extruding the viscose into an aqueous spinning bath containing from. about 16% to sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the percentage sulfuricacidcontent of the spinning bath exceeding the slubbing point but not exceeding about 1.36 times the percentage caustic soda content of the viscose.

References Cited in the file of this patent V V V UNITED STATES PATENTS Schuette Oct.;3, 1939 2,312,152 Davis Feb. 23, 1943 2,373,712 Schlosser Apr. 17, 1945 2,535,044 2 Cox Dec. 26, 1950 2,593,466

MacLaurin Apr. 22, 1952 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRODING VISCOSE CONTAINING FROM ABOUT 0.5% TO ABOUT 4%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF AN ALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHER OF P,P''-DIPHENOL INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 2K% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINE SULFATE AND SULFURIC ACID, THE PERCENTAGE SULFURIC ACID CONTENT OF THE APINNING BATH EXCEEDING THE SULBBING POINT BUT NOT EXCEEDING ABOUT 1.36 TIMES THE PERCENTAGE CAUSTIC SODA CONTENT OF THE VISCOSE. 